Optical Transport Networks (OTNs) provide functionality including transport, multiplexing, switching, and management of optical channels carrying client signals. Packet-optical integration between electrical and optical domains of a communication network is an important challenge in the implementation of optical networking. One option is to implement the packet-optical integration within a Software Defined Network (SDN) environment, with a single SDN controller responsible for discovering and controlling both the packet and optical domains.
Various mechanisms exist to allow auto-discovery of the links internal to the different domains. For example it is possible to have an SDN controller passively listen to the IGP/BGP routing instance of each domain and so learn its topology. There are also mechanisms, such as LLDP or LMP, which enable links connecting different domains, also known as border links, to be discovered. However, these mechanisms are limited to discovering links within the same layer or switching capability.
In a packet-optical environment the end points of border links are the line card of the router in the electrical domain and the client port of the optical transponder in the optical domain. The client ports of the transponder are not able to process any type of packet such as Ethernet frames or IP packets, and these ports are not therefore able to run any protocol to enable link discovery. Auto-discovery of data plane connectivity between routers and optical devices is not therefore possible. The only way to populate a multilayer database of border links is to let the routing protocols populate single layer databases and then manually enter the information regarding the connectivity between layers.